1. Field of the Invention
This invention relates to a signal distribution system for multiband and multidirectional antennae arrays.
2. Description of the Prior Art
One of the primary and most effective antenna used in radio-reception involves a circularly diposed phased array antenna which typically features a series of three array elements as illustrated by the FIG. 1 representative of a AN/FLR-9 antenna manufactured by GTE Sylvania.
The AN/FLR-9 covers a frequency range of 2-30 MHz with the Band A group of antenna elements producing a set of beams in the range of 2-6 MHz, the B band elements producing a set of beams in the 6-18 MHz range and the C band producing the third set of beams having a frequency range of 18-30 MHz. In this way the circular disposition of the antenna array allows for 360.degree. coverage in three separate frequency intervals making up the total from 2-30 MHz. Each band A, B or C is developed by a predetermined number of elements as for example 96 which are taken at 16 element outputs at a time for a particular direction. These 16 outputs go to a beam forming circuit. The next set of outputs develop an output beam from another 16 elements which are oriented in a slightly different manner. This second output series of elements substantially overlap the elements used in developing the first output beam but include at least one additional element not considered in the previous or first output. Thus it can be seen that the total set of beams formed for example in Beam A is developed from a total of 48 elements taken 16 at a time for example. This method allows for a total beam structure to be developed which is respective of signals from an entire 360.degree.. The beam elements for the B band and the C band operate similarly with perhaps differing number of elements. The other structures shown in the FIG. 1 are addressed to the reflecting screens for the band which as shown in the Figure have a single reflecting screen for both bands A and B and a separate reflecting screen for the C band antenna elements.
One of the difficulties with the use of this particular type of phased array system is that the output from the beams in each of the bands A, B, and C must be individually fed to an output distribution system having a port for each of the individual beams in bands A, B and C. The reason for this separate requirement for three ports is related to the difficulties which previous attempts to combine antenna beams have had covering adjacent frequency bands. That is the beams in bands A and B could not be combined to a single distribution port because it had been assumed that beams oriented in nearly the same direction would be combined and would cause difficulty at the cross-over frequencies. These cross-over frequencies, at which the two beams which are combined have approximately the same voltage gain, produced combined signals which could possibly cancel each other out in the combining network. This can be best explained by visualizing the A band covering a frequency between F1 and F2 and the B band covering a frequency between F2 and F3. At a certain point in the gain voltage some of the frequency of the interval between F2 and F3 would be picked up by the A band beams because of overlap and simultaneously some of the frequencies in the F1 to F2 interval would be picked up by the B band beams due to the same overlapping feature. When these two signals are combined in a combining network the possibility exist that the signals which were caught by the overlapping A band would be mixed with the signals caught by the overlapping B band and due to the configuration may possibly be cancelled in the combining network, thus leaving a frequency gap.
Due to these difficulties the prior art required an output distribution port of a signal distribution system for each of the beam A, B, and C arriving from the phase antenna array structure. It is to this specific problem that the present invention addresses its distribution system and method.